This invention relates to a high-frequency heater using a magnetron to execute dielectric heating, such as a microwave oven, and more particularly to an inverter power unit for converting a commercial power supply into a high-frequency, high-voltage power supply for driving a magnetron.
Hitherto, for the inverter power unit for converting a commercial power supply into a high-frequency, high-voltage power supply for driving a magnetron, the Unexamined Japanese Patent Application Publication No. Hei 5-121159 discloses a monolithic voltage resonance inverter of a single-terminal type. The inverter power unit converts power converted into a high frequency by the inverter into a high voltage through a step-up transformer and generates a high DC voltage appropriate for driving the magnetron by a high-voltage circuit using multiplication voltage rectification or a rectifier circuit, whereby the step-up transformer can be miniaturized by converting power into a high frequency by the inverter and the circuitry is formed on a single board, so that a compact and lightweight magnetron drive power supply (inverter power supply) can be provided.
FIG. 6 is a block diagram of inverter circuitry in related art from the top thereof. In the figure, numeral 1 denotes an inverter block implemented as an inverter, numeral 2 denotes a control block for controlling the inverter, numeral 3 denotes a step-up transformer block, and numeral 4 denotes a high-voltage circuit; the parts are mounted on one printed circuit board 5 for providing a compact and lightweight configuration.
However, there is a problem of widening the circuit mounting area to provide the insulating distances of a high-voltage circuit as a factor of impairing the merits of miniaturization. FIG. 7 is an external view to show the high-voltage circuit portion. The high-voltage circuit 4 is made up of high-voltage diodes 6 and 7, high-voltage capacitors 8 and 9, a tab terminal 11 for connecting a lead for feeding power into a magnetron filament, and a discharge resistor 10 for discharging high-voltage charges charged into high-voltage capacitors 8 and 9 when the magnetron fails. A high voltage of 3 to 4.5 kV or transiently about 7 kV occurs between the terminals of the parts making up the high-voltage circuit 4. of course, the high-voltage circuit 4 must be designed with appropriate insulating distances to provide insulation. Assuming also the possibilities of deposition of dust and moisture absorbed in the dust because of dew condensation thereon, etc., the insulating distances with a more margin are required and the mounting area of the high-voltage circuit 4 becomes fairly wide. Thus, the circuitry mounting area cannot be miniaturized; this is a problem.
It is therefore an object of the invention to provide a magnetron drive power supply comprising: a step-up transformer for stepping up output of the inverter section, and a high-voltage circuit comprising two high-voltage capacitors in bare-chip status and two high-voltage diodes for a full-wave voltage doubler rectifying output of the step-up transformer, wherein
the high-voltage circuit is provided as a unit molded of a resin.
According to an aspect of the invention, there is provided with a magnetron drive power supply comprising:
a unilateral power supply for converting a commercial power supply into a unilateral power supply,
a rectification filter section for rectifying and smoothing the unilateral power supply,
an inverter section for converting the unilateral power supply provided through the rectification filter section into a high-frequency AC voltage as at least one semiconductor switching element is turned on/off,
a step-up transformer for stepping up output of the inverter section, and
a high-voltage circuit comprising two high-voltage capacitors in bare-chip status and two high-voltage diodes for a full-wave voltage doubler rectifying output of the step-up transformer, wherein
the high-voltage circuit is provided as a unit molded of a resin.
According to the invention, while the parts making up the high-voltage circuit are brought close to each other, are connected, and are integrated at a high density, the insulation performance of the high-voltage circuit can be provided because of the resin mold, a compact magnetron drive power supply can be provided, and a machine chamber can be made small. Thus, a high-frequency heater having a compact outside shape and enlarged oven dimensions can be provided and the user""s flexibility of installation can be enhanced.